Variable pitch airscrew



March 16, 1943.- Gv. ALGARssoN K 2,313,795"

VARIABLE FITCH IRSCREW Filed Aug. 12, 19:52:v e sheets-snm 1 GRfrrlR/llcnkssaN Vrrofensy.

March 16, 1943.

VARIABLE FITCH AIBscREw y' AFiled Aug. 12, 193B f f 6 sheets-sheet 4 TTUKNE/ yca.I LG'ARssoN 2,313,795

March 16, 1943. G. ALGARssoN Y '2,313,795

l I VARIABLE FITCH AIRSCREW A n 'V Filed aug. 12, 19:58 6 sheets-sheet 5 arrok/vf/ Patented 16,V 1943 UNITED STATES PATENT OFFICE VARIABLE FITCH AIRSCREW V('rettir Algarsson, Montreal, Quebec, Canada, assignor to Algarsson Engineering Company Limited, Montreal, Quebec, Canada 4 Application August 12, 1938, Serial No. 224,449

' In Canada June 2, 1938 Thisinvention relates tolvariable pitch airscrews and seeks to provide means whereby the R. P. M. of the airscrew may be maintained at any selected value through variation of the pitch setting of the airscrew blades.

According to the invention a balance is established betweenthe twisting moments in the blades, modied by centrifugal means, and torque transmitted-through a gear train to or from al governor controlled mechanism.' This governor controlled mechanism may consist of pneumatic or hydraulic pumps or motors, or` of their elecl trical equivalent.

The use of the invention enables the operator of an aircraft to use the full power of the engine under all conditions. At will the operator may reverse the thrust of the airscrew thus providing an effective air brake. The airscrew blades can 16 Claims. (CL T10-163) throttle valves showing one valve closed and the other open.

Figure 'I is a view similar to Figure 6 but showing the valves in the reverse position.

Figure 8 is a sectional side elevation of a two bladed airscrew hub mounted on a splined shaft. Figure 9 is a sectional front elevation on the line 9-9 of Figure 8.V

Figure- 10.is a side elevation of an airscrew having a hub similar to that shown in Figures 1 and 2-but employing a single pump to reduce the pitch in opposition to overbalancing counterweights. A

Figure 11 is a side elevation of an airscrew having a'hub similar to that shown in Figures 1 and 2 but employing gear pumps in'place of the reciprocating type. Figure 12 is a diagram showing the relation of the various forces acting on a bladein the case of an airscrew "employing a pump-motor and a compressor. The pump-motor is shown operating as a 'comprson Figure 13 is a diagram similar to Figure 12 -l but shows the pump-motor acting .as a motor.

torque reaction, and is constantly driven" by the rotation of the airscrew..

In order that the'inventioxi may be more readily understood reference, is made to the drawings inl which Figure 1 is a sectional side elevation of a two bladed airscrew' employing a pumpmotor and a compressor with the valve mechanism in the neutgal position and indicating the engine in the outside elevation.

Figure 2 is a sectional front elevation on the line 2-2 of the airscrew hub shown in Figure 1.

Figure 3 is a partial sectional view of the pump-motor showingl the location of. the exhaustv port. the arrows indicating the iiow of the air during the exhaust stroke, the' pistons and connecting rods being shown in dotted lines.

Figure 4 is a view similar to Figure 3 but showing thelocation ofthe inlet port and the iiow of air during the intake stroke.

Figure 5 is a view similar to 3 and 4 but shows both exhaust and intake ports closed, the piston ailected being shown4 dotted at both top and Figure 141s a diagram showing, the relation of the various forces acting on ablade in the case oi':an airscrewemploying a pump and an overbalancing counterweight. i Y

Figure l5 is a diagram similar to Figure 13 but showing the blade in a negative position and receiving reverse thrust.

Figure 16 is a graph illustrating generally the aerodynamic and centrifugal moments gener? ated in the blades and in the eccentric weights. Figure 17'is a'section at the lineil of Figure 8 showing the eccentric weights only in full lines,

1 the upper weight being in section.

The device shown and described in this application is an improvement upon the device shown and described in my co-pending application for Patent Serial No. 174,514, flied November 15, 1937.

Referring to the drawings, vthe engine shaft I5 has a tapered end IB on whichis keyed the anged sleeve I1. This sleeve *I1 is retained on the tapered end of the shaft i5 b y means of the keeper nut Il, which in turn is locked b'y the locking ring I9.

Mounted on the ne've n is the rear han zo.

of the hub casing which has a iiange 2| bolted rear half 20. The airscrew blades 26. The centrifugal pull of the'blade is trans',-

I 24 Aaudit are'anchored' directly to each other through'V the ball bearings of blades decreases.

mitted to the inner races of the bearings 26 through the axial pin 21 and its head 26. Tl'lis centrifugal pull is balanced by that of the opposite blade 25 transmitted to the outer races of the bearings 26 through the sleeve 29 and its shoulder 30.

The blades 24 and 25 are located in the hub casing by the bearings 3| which transmit all the bending loads from the blades to the hub casing and are adjusted by the adjustment rings 32 which latter are secured in-any desired setting y by the locking keys 33.

The adjustment rings-32 provide a means of preloading the bearings 26 and 3| and at the same time permit accurate balancing of the Whole airscrewby slackening one adjustment ring and tightening the other, thus displacing both blades and the ball bearings 26 in the same direction along their. common axis.

In the above arrangement the common axis of A the blades is forward of the end of the engine shaft. Figures 8 and 9 illustrate a variation applicable when it is desired. to penetrate the centre of the hub or when three or more blades are to be employed.

Each ofthe bevel gears 34 carries a weight; 31 V located eccentrically with regard to the axis of the blades within the hub casing.

As theblades turn about theirvaxes towards high pitch the weights 31 turn with them approaching the plane of rotation of the airscrew. The distance between each weight 31 and the airscrew axis, therefore, increases as the pitch of the blades increases and decreases as the pitch The centrifugal force generated in these weights by the rotation of the airscrew varies directly as the distance from the airscrew axis, R. P. M. being constant andi tends always to turn the blades to a higher pitch setting.

Aual rotation of the internal gear 38 in relation to the internal gear 46 out in the hub casing. Rotation o f the internal gear 38 and the bevel gears is attended by proportional rotation of the planetary gear ring 4|. This proportion or ratio depends on the pitch diameters of the planetary gears and the internal gears with which they mesh; thus providing a compact and robust gear train, giving the planetary gear ring 4| a mechanical advantage over the bevel gears and through them the blades. Rotation of the planetary gear ring is transmitted to the drive ring 44 through the spurs 42 and 43. v

The various gears comprising the rst stage of the gear train moves V in relation to each other only when the airscrew blades are changing pitch. At all other times, when the airscrew is rotating, they operate in a static condition transmitting from the drive ring 44 whatever torque is necessary to maintain the pitch seti-ing. The second' stage ofthe gear train, which is consstantly running, consists of the reducing gears 5| and 52, the idler gear 53 and the gear 54.. The gear 5| meshes with the gear 55 cut in the drive ring 44 and is connected with the gear 52 by the shaft 56. The rotation of the gear 52 is transmitted to the gear 54 through the idler gear The gear 54 is mounted on the crank shaft 51 of a pneumatic pump-motor 58 which,in the form of the invention illustrated Vin Figure 1, is the mechanism producing torque reaction.

The whole gear train including both stages is permanently connected and can `at any moment transmit drive from either end between the airscrew blades and the pump-motor.

. to an inlet port 6| in each of the cylinders 62.

Cut in the rear face of the bevel gear 36 is thev 1 .The first stage is composed of the Planetary l gears 39 and 46, the 'planetary gear ring 4|, the

' spur gears 42and 43 and the drive ring 44. The

drive ring 44 is journalled on the sleeve |1. The planetary gears mesh with the internal gear 36 and -are connected throughthe shafts 45 with Each piston 63 acts as a slide valve controlling the intake and discharge of an adjacent cylinder. Each cylinder 62 is provided with a duct 64 leading from the cylinder head to the port S5 in the wall of an adjacent cylinder on one side, and on the other side has in its own wall apart 65 leading to the head of the other adjacent cylinder through its duct 64. A recess 66 in each piston 63 connects the inlet Vport 6| with the port 65 when the piston is below the half stroke position. Figure 4 illustrates diagrammatically this position, the arrows indicating the flow of air the planetary gears 40 which mesh with -the inlternal gear 46 cut in the 'rear half 20 'of the hub "Theyspur gears 43 mesh with the gear 50 on the Adriv'ejring 4 4 thus completing the nrst stage-of the'gear train. Y

'The planetarygears 39 are of slightly'larger from the intake manifold and the direction .of-

movement ofthe piston affected. Figure 3 illustrates a position inv which the piston acting as a slide valve is above the half stroke point. The

inlet port 6| is now covered by the piston skirt 61 and the port 65 is open to the crank case 59,'

thus permitting air to pass from the cylinder affected to the crank case during the exhaust stroke. Figure 5 illustrates the half stroke position of the piston acting as a slide valve and shows both ports 6| and 65 closed. As indicated in this figure,l this position occurs at `ooth top VAPitchcontrol o! the airscrew the discharge line to a throttle valve 13. An

exhaust line 1l leads from the crank case lt ot the pump-motor 5B to another throttle valve 1I.

The throttle valves 1l and 1I form a part of the valve stem IM in the Lengine driven governor 16 and are so arranged that vwhen the governor is at mid stroke both throttle valves are wide open. As the governor responds to increased speed the valve stem Ilii moves upward against the pressure of the spring 1s closing the throttle valve and leaving the throttle valve 13 wide open. This position o! the throttle valves is illustrateddiagrammatically in Figure 6. As the governor responds to reduced engine speed the valve stem Ilil moves downward under pressure o! the spring 19 opening the throttle valve 15 and, reaching the full open position at the mid stroke or the governor. As the governor continues to respond to decreasing engine speed the throttle valve 13 closes, leaving the throttle valve 15 open. This latter position of the valves is illustrated diagrammatically in Figure 7.

The throttle vvalves 13 and 1l each have four outlet ports numbered 11 and 1I respectively.

'I'he diameter of each outlet port is halt that of the single Vinlet line 12 or 14. 'I'his arrangement halves the length 'of stroke of the valves and connn'es the throttling tothe outlet ports.

The setting of the governor 1l is adjusted by varying the setting of the spring 19. This variation is accomplished by manual remote control of the worm lll.

A remotely controlled 'lever .Il is provided by.

a relief valve 84. A A branch line I5 leads fromV a compressed air reservoir to the exhaust line 1l. A valve 81 controls the flow of air from the reservoir 86 to the branchline li which is provided with a pressure gauge Il within of the pilot.

Operation of the 4propellingv unit of Figure 1 In the operation of this invention, the twist;

ing moments generated irlf the eccentric weightsy 31 nearly balance the resultant of the aerodynamic and centrifugal twisting moments produced bythe blades themselves. Owing to the arrangement of the blade mountings, the friction opposing change of pitch is reduced to a l minimum, so that the load on the gear train under normal running conditions is reduced to alow value, being only that amount required to correct the balance of twisting moments `plus the minimized friction. -A

through thegear trainin the followingzmanner:

The governor 'is adjusted by the operator to any desired value of R. P. M. by means of the remotely'c'ontrolled worm IQ.' It theR. P. M. rise jabove this desired-value the governor" moves A lf'thejvalve 'stemill Acarrying the valves 1Q and 1iupward closingthe ports Hand-leaving the ports 11 wide open. The discharge otthepump the view biases is effected motor is thus' restricted and pressure built up in the exhaust line 1l and the crank case 58. ,The imp motor lli is now under load as a compressor and a torque reaction or drag is applied through the constantly running second stage of the gear-.train to the drive ring M. "The drag on the drive ring 44 is transmitted through the rst stage of the gear train andthe'bevei gears to the airscrew blades, turning them to a higher l0 pitch setting,4 increasing the load upon the engine and thus arresting increase in R. P. M. The gear ratio provided by l'the planetary gearing, located in the rst stage of the gear train operates to convert a small drag upon the drive ling into a comparatively large twisting moment tending to change the pitch oi the blades; it also serves l to minimize suddenor uneven pitch changing movements.

If the R. P. M. fall below the desired value the spring 19 moves the valve stem I 0i downwards closing the ports 11 and leaving the ports 1l wide open. The discharge of the pump motor BI is now unrestricted andthe discharge of the compressor4 B8 is applied to the intake of the pump mtol's i 'I'he compressor 68 runs faster than the pump motor 58 and consequently the air discharged vby w it is forced under pressure through the intake of the pump motor thus causing the latter to act.

the blades to a lowerpitch setting, relieve the- 4- load upon the engine and thus arrest decrease in R. P. M. l-

In other words by loading the pump-motor I8 as a compressor, a torque reaction is transmitted to the blades dragging them into a higher pitch setting, lowergpitch settings being achieved by loading the pump-motor vi8 as an air motor, thus causing it to overrun the gear train andapply 40 torque to the .blades in the opposite sense.-

' The arrangement of the pump-motor shown,

in which the intake and exhaust ports open and close on dead centres of the pistons affected, is

advantageous as any leg or lead which might suit the operation of the pump-motor as an air motor would interfere'with its operation as a mpressor or vice-versa.

'I'he governor will continue to correct the engine R. P. M. to thedesired value through alteration of pitch, and consequently of loadupon the engine, regardless of the cause' of variation.

The graph in Figure 16 shows approximately the relative magnitude of the twisting moments acting upon a blade in a typical case.` The loads. v

on the gear train appear in this graph as the vertical distances between two curves. lThe curve A shows the aerodynamic twisting moments occui'ring at various pitch settingswith power out:

put, R.- P. M. and air density constant. The

torque due to the action of centrifugal force on curves already described, and the Vcurve CV shows the centrifugal twisting moments" impartedy by the eccentric weight l1.

As the curve +I represents twisting moments tending to reduce the pitchand thecurve C represents twisting moments tending to increase pitch, the vertical distances between the two indicates the twisting moments to be supplied by the torque producing mechanism in order to correct the balance. When changingpitch a small 'l5 additional load wouldbe placed upon the torque curve I indicates the magnitude of' inherent the blade.

trifugal in nature, will vary as the square of the R. P. M. The Values indicated by curve A are aiected by other variants but are smaller.

-The` loads on the gear train, therefore, should not greatly exceed the proportions indicated.

The diagram in Figure 12 shows therelation of the various forces acting on a blade, when the valve 15 is closed, the valve 13 open and the Dump-motor 58 acting' as a compressor. line C indicates the direction of the centrifugal twisting moment exerted by the eccentric weight 31, I indicates the direction of the inherent torque due to the action of centrifugal force on the blade, C. P. indicates the position of the centre of pressure, which in this case is shown on the'trailing edge side of the axis of rotation of the b lade thus applying a twisting moment in the direction ofthe line marked thrustj and 'A indicates the position of the axis of rotation of The arrows on the pumpmotor 58 indicate its direction of rotation and F indicates the direction of the torque reaction transmitted to the blades through the gear train.

Figure 13 is simliar to Figure 12 but illustrates the condition Awhen the valve 15 is open, the valve 13 closed and the pump-motor 58.0perating as a motor, F indicates the direction of the drive of the pump--motorv 58, acting as a motor, transmitted to the blades through the gear train.

In the form of the invention illustrated in Fig- I ure 10, in which a single pump is employed in conjunction with overbalancing counterweights, the discharge line 14 is connected to the valve 13, and the compressor 68 and valve 15 are elimiengine is so farthrottled down that it can only maintain the desired value of R. P. M. with the load at a minimum. The pilot closes the throttle still further and the R. P. M. of the engine will fall below the desired value regardless of the pitch setting of the blades.v The governor however will continue to close the valve 13 as long l as the R. P. M. are below the desired value forcing theblades into a lower pitch setting and causing the thrust to reverse. This increase the load on the engine slowing it down and causing the governor to close the valve 13 even further. This sequence of reduced pitch attended by increased load and reduced R. P. M. is cumulative and results in the blades being turned to their extreme low pitch setting. prevented from going to any lower pitch setting by suitable stops on the inside of the hub casing but not shown. If the pilot now reopens the throttle, the engine will be under a heavy load, producing reverse thrust, and will be unable to regain the desired value of R. P. M. to which the governor is adjusted. 'The governor will continue to keep the valve 13 closed andthe blades will remain in their extreme lovl1 pitch setting regardvless of manipulations of the throttle. In other words the pilot can use the engine as a brake 'to any extent within its power without fear of its normal condition of forward thrust, the pilot nated. The governor 16 operates the valve 13 in .the manner already described but causes the pump-motor 58, acting as a compressor, to drag the airscrew blades towards low pitch' against the action of the eccentric weights 31, which lat-l an air brake.

Figure 14 is used as closes thelthrottle, operates the lever 8| and then reopens the throttle. The mechanical operation is as follows: Whenthe pilot closes the throttle, the R. P. M. of the engine fall ol regardlessof the pitch setting of the blades. AVlhen he operat'es the lever 8| he opens the valve 13 and closes the valve 15, causing the pump-motor 5t', acting as a compressor, to turn the blades te tl eir extreme high pitch setting. This extreme high pitch setting'is the feathered or infinite pitch position.

When the pilot .reopens the throttle, the

R. P. Mfof the engine will increase and when he releases the lever 8| the governor will again close the valve 13 causing the pitch of the blades to decrease until a pitch setting giving normal forward `thrust is reached.

A furtherfeature of the invention is that in the event o/f engine stoppage from any cause the pilot can cause the blades to turn to the feathered position, thus reducing drag 'and losses due to vturbulence of the air flowing over adjacent portions of the wings. This can be accomplished, if the engine has not ceased torevolve. by operating the lever 8| in the manner just described A feature of lthe invention using the above described mechanism is that the pilot can at any time move the blades into their extreme low pitch setting` and use vthe enginefas a brake. This is accomplished by closing the throttle and then opening it again, the sequence of operations being as follows: Y

The pilot closes the throttle, thereby reducing the R. P. M. of the engine. 'Ihe governor automatically closes the valve 13 thus causing the pump-motor 58 to act as a motor thereby turnan air motor in a direction opposite to itsI normaland keeping it in operation until after the engine has stopped. If the tengine has already ceased 4to rotate, the blades lcan still-be moved .into the feathered position by operating the lever 8| and then opening the valve and permitting compressed air to flow from the reservoir 86 to the exhaust -line 14 and the crank case of the pump-motor 58, thus causing the latter to act as rotation and turn the blades into the feathered position. In this case the air exhausted from the pump-motor 58, operating'as a motor in reverse, escapes through the valve 13'whichiis opened by the same' operation of the lever 8| which closesv the valve 15. j

This invention has been described as applied The blades. are

A for the use of the reservoirl 85, as the blades will ing type of blade has a tendency to respond auto- 4identical functions. The relief valve 95 isfitted between the lines and 1l protecting the former 1s wiuithe return une s1 thus special plan form in which the centres of pressure along the blades are on thetrailing edge side ofthe axis of rotation. When using blades of the last mentioned variety there is no necessity automatically feather on the principlel of the weather vane, and the lever 8l will be necessary 'only when it is desired to resume forward thrust after using the engine as a brake. This feather- '10 matically to variations in airspeed, altitude, etc. imposing less load on the pitch controlling mech- In the form of the hub illustrated in Figures 8 and 9 the engine shaft I5 has a splined end 89 on which both halves 2li and 23 of the hub casing are i mounted byy means of cones 90. The

' blades 24 and 25 are located in the hub casing in the same manner as illustrated in Figures 1 and 2 but, in place of the common central bearing 2 8, bearings 9| transfer the centrifugal pull of each blade to an anchoring barrel 92 'which encloses the splined shaft but does not bea-r upon it or the hub casing. This structure can be further modiiied to accommodate three cr more blades. In both forms of blade mountings shown,

f the blades .and their centrifugal bearings and attachments are assembled separately and inserted as a unit in place against the rear half of the hub casing.

In the foregoing description, air pumps orV a combination of air pumps and air motors have been described as the sources of the torque reaction.' It will be understood that these pumps and motors could be adapted to employ any gaseousvmixture, or could be hydraulic employing oil or other fluids as an operating medium They could also be replaced by generators and motors employing electricity, without altering the general-arrangement or efficiency of control. In the latter case, rheostats or some other load varying device would be substituted for the va'ives referred to.

L' v peratonl of the form of Figure 11 The principle of operation in this form of the invention is identical with that of the form illustrated in Figure 1, the differencesare purely mechanical and consist in the substitution of gear pumps for the reciprocating variety, the addition of relief valves protecting the system from excessive pressures and the provision `of return lines closing the system. f

A gear `pump 93 occupies the same position and performs the same function 'as the pump motor 5,-,

.il illustrated in Figure 1, an'd a gear pump 94 similarly takes .the place of the compressor B8. The pipe lines 10, 12 and 14 are arranged in the same way as illustrated in Figure l and fulfill lagainst excessive pressure by providing a bypass. In the same way a relief valve 96 protects the line 1I. A return line 91 connects the discharge of the relief valve 99 with the intake 98 of the pump 9i. Further return lines 99 and |09 connect the discharges of the valves 13 andclosing the pump screw which may be set to run at any value of R. P. M. selected by the pilot', in which the blades may be feathered in the event of engine stoppage," which may be made to develop reverse thrust at the will of the pilot and employed either as a brake or as an aid to maneuvering onthe ground, or, in marine aircraft, the water: which is positive in action, using as it does direct mechanical connection between the rotating airscrew and the statically mounted. control means and cenilning to the latter the selected media of operation whether pneumatic', hydraulic or electric.

What I claim is:

1. In a variable pitch airscrew of the kind in which the blades of the airscrew are connected together to effect equality or pitch setting. a counterweight nearly balancing the 'aerodynamic and other forces acting on each blade, a gear train capable of transmitting rotation from either end and connected -at one end with the airscrew blades, a statically mounted torque producing mechanism connected with the other end of said gear train for pitch changing movement oi' the blades, said gear train containing a reducing gear carried by the hub and giving the torque'producing mechanism a mechanical advantage over the airscrew blades. and means to control said mechanism to vary the torque produced both in magnitude and direction to effect increase or decrease of pitch setting of the airscrew blades.

2. In a variable pitch airscrew of .the kind in which the blades of the airscrew are connected together to 4effect equality of pitch setting, a counterweight nearly balancingthe aerodynamic `and other-forces acting on each blade, a gear train capable of transmitting rotation from either end and connected at one end with the airscrew blades, a'. statically mounted torque producing mechanism connected with the other end' of said gear train for pitch changing movement of the blades, said gear train containing a reducing gear carried by the hub and givingthe torque producing mechanism Aa mechanical advantage over the airscrew blades, means to'control said mechanism to vary the torque produced both in magnitude and direction to effect increase or decrease of pitch setting of the airscrew blades, and a governor controlling said means Ain agreement with variations in rotational Vspeed of the airscrew from a selectable datum.

3. In a which the blades of the airscrew are connected together to effect equality of pitch setting, a counterweight nearly balancing the aerodynamic and other forces 'acting on each blade, a gear train capable of transmitting rotation from either end and connected at one end with the airscrew blades, a statically mounted air pump, which may be operated as a motor, connected with the other end of said gear train for pitch changing movement of the blades, a compressor adapted to de-v liver air to the intake of said air pump, meansv to control the intake or discharge of said pump to vary the magnitude or reverse the direction of the torque applied by s aid pump to the gear train to effect increase or decrease' of pitch setting of the airscrew blades, and a governor controlling said means in agreement with variations in rotational speed of the airscrew from a selectable datum.

44. nr a variabie pitch airscrew of thekind in l which the blades of the airscrew are connected together to eect equality of pitch setlfflll.V a

variable pitch airscrew of the luna'in`l counterweight nearly balancing the aerodynamic andother forces acting on each blade, a gear train capable of transmitting rotation from either end and connected a't one end with the airscrew blades, a hydraulic statically mounted pump, which may be operated as a motor, connected with the other end of said gear train for pitch changing movement of the blades, a second hy,- draulic statically mounted pump having its discharge connected to the intake of the iirsthydraulic pump, means to control the intake or discharge of said iirst pump to vary the magnitude or reverse the direction of the torque applied by said pump to the gear train to effect increase or decrease of pitch setting of the air screw blades, and a governor controlling said means in agreement with variations in rotational speed of the airscrew from a selectable datum.

'5. In a variable pitch airscrew of the kind in which the blades of the airscrew are connected together to eilect equality of pitch setting, a counterweight nearly balancing the aerodynamic and other forces acting on each blade, a gear train capable of transmitting rotation from either end and connected at one end with the airscrew blades, said gear train comprising two stages, the ilrst of which is carried by the airscrew and gives the second stage a mechanical advantage over the to control the intake or discharge of said pump to vary the magnitude or reverse the direction of the torque applied by said pump to the gear train to eiect increase or decrease of pitch setting of the airscrew blades, and a governor controlling said means in agreement with variations in rotational speed of the airscrew from a selectable datum.

6. In a variable pitch airscrew of the kind in which the blades of the airscrew are connected together to eil'ect equality oi'- pitch setting, a counterweight nearly balancing the aerodynamic and other forces acting an each blade, a gear train capable of transmitting rotation from either end and connected at one end with the airscrew -blades,' said gear train comprisingy two stages, the iirst of which is carried'by the airscrew and gives the second stage a mechanical advantage over the blades, a drive ring rotatable about the airscrew axis connecting the two stages of the gear train', a statically mounted air pump, which may be operated as a motor, connected with the other end of said gear train for pitch changing movement of-the blades, a compressor adapted to deliver air to the intake of said air pump, means to control the intake or discharge of said pump to vary the magnitude or reverse the direction of the torque applied by ,said pump to the gear train to effect increase or decrease of pitch setting of the air screw blades and a governor controlling said means in agreen'lent` with variations in rotationalsp'eed of the airscrew from a selectable datum.

7. In 'a variable pitch airscrew of the kind in which the blades'of the airscrew are connected a planetary gear system located concentrically in relation to the airscrew axis and giving the second stage a mechanical advantage over the blades, a drive ring rotatable about the airscrew axis connecting the two stages of the gear train, a statically mounted air pump, which may be operated as a motor, connected with the other end of said gear train for pitch changing movement oi' the blades, a compressor adapted to deliver air to the intake of said air pump, means to control the intake or discharge of said pump to vary the magnitude or reverse the direction of the torque applied by saidpump to the gear train to effect increase or decrease of pitch setting of the airscrew blades, and a governor controlling said means in agreement with variations in rotational speed ofthe airscrew from a selectable datum. l

8. In a variable pitch airscrew of the kind in which the blades of the airscrew are connected together to effect equality of pitch setting, a counterweight nearly balancing the aerodynamic 'and other forces acting on each blade, a gear train capable of transmitting rotation from either end and connected at one end with the airscrew blades, said gear Ytrain comprising two stages, the first stage, carried by the airscrew, containing a planetary gear system located concentrically in relation to the airscrew axis and giving the second stage a mechanical advantage over the blades, a drive ring rotatable about the airscrew axis connecting the two stages of the gear train, a statically mounted air pump, which may be op-l erated as a motor, connected with the other end of said gear train for pitch changing movement of the blades, a compressor adapted. to deliver air to the inake of said air pump, means to control the intake or discharge of said pump to vary the magnitude 'or reverse the direction of the torque. applied by said pump to the gear train to 'effect increase or decrease of pitch setting of the airscrew blades, a manual control to the intake or discharge of said pump to cause said pump to apply a torque through the gear train to the airscrew blades turning them to their extreme high pitch or feathered position, and

a governor controlling said means in agreement with variations in rotational speed of the airscrew from a selectable datum. i

9. In a variable pitch airscrew of the kind in which the blades ofthe airscrew are connected together toV eiect equality of pitch setting, a counterweight nearly balancing the aerodynamic and other forces acting on each blade, a gear train capable of transmitting rotation from either end and connected at one end with the airscrew blades, said gear train comprising two stages, the rst stage, carried by the airscrew, containing a planetary gear Isystem located concentrically in relation to the airscrew axis and giving the second stage a mechanical advantage over the blades, a. drive ring rotatable about the airscrew of said gear train for pitch changing movement together to etlect equality of pitch setting, a

end and connected at one end with the airscrew 1 blades, said gear train comprising two stages, the iirst stage, carried by the airscrew, containing of the blades, a compressor adapted to deliver air to the intake of said air pumpa relief valve on lthe discharge side of said air pump, means to control the intake or discharge of said pump to vary the magnitude or reverse the direction of the torque applied by said pump to the gear train to effect increase or decrease of pitch setting of the vairscrew blades, a manual control to the intake or discharge ofsaid `pump to cause said pump to apply a torque through the gear train to the airscrew blades turning them to their extreme high pitch or feathered position, and a governor controllingsaid means in agreement with variations in rotational speed of the air screw from a selectable datum. Y

10. In a variable pitch airscrew of the kind in which the blades of the airscrew are connected together to effect equalityi of pitch setting, a counterweight nearly balancing the aerodynamic and other forces acting on each blade, a gear train capable of transmitting rotation from either end and connected at one end with the airscrew blades, said gear train comprising' two stages, the `first stage, `carried by the airscrew, containing a planetary gear system located concentricaliy in relation to the airscrew axis and giving the second stage a mechanical advantage over the blades, a drive ring rotatable about the airscrew axis connecting thel 'two stages of the gear train, a statically mounted air pump, which may be operated as a motor, connected with the other end of said gear train for pitch changing other end of said gear train for pitch changing 'movement of the blades, said mechanism comprising a plurality of fluid pressure means connected together and'adapted to be operated either as a pump or as a iluid motor and means to control said mechanism to vary the torque produced both in magnitude land direction to effect increase or decrease of pitch setting of the airmovement 'of the blades, a compressor adapted to deliver air to the intake of said air pump, a

relief valve on the discharge side of said air pump, means to control the intake or discharge of said pump to vary the magnitude or reverse the direction of the torque applied by. said pump to the gear train to effect increase or decrease of pitch setting of the airscrew blades, a charged reservoir connected to the discharge of the air pump adapted to be used therewith to turn the blades to their extreme high pitch or feathered position, a manual control to the intake or discharge of said pump to cause saidpump to apply a torque through the gear train to the airscrew blades turning them to their extreme high pitch or feathered position, and a vgovernor controlling said means in agreement with variations in rota-v tional speed of the airscrew from a selectable datum.

11. In a variable pitch airscrew having two blades rotatably mounted on a hub casing and connected together to effect equality of pitch setting. a common central bearing taking the centrifugal pull of both blades, a counterweight nearly balancing the aerodynamic and other forces acting on each blade, agear train capable of transmitting rotation from either end and connected at one end with the airscrew blades, said gear train comprising two stages, the first stage, carried by the airscrew, containing a planetary gear system located concentrically vin relation to the airscrew airis and giving the second stage a mechanical advantage over the blades. a drive ring rotatable about the airscrew axis connecting the two stages of the gear train, a statically mounted air pump, which may be operated as a motor, connected with the other end of said gear train for pitch changing movement of the blades, acompressor adapted to deliver air to the intake of said air pump, means to control the intake or discharge of said pump to vary the magnitude or'reverse the direction of -the torque applied by said pump'to the gear train to effect increase or decrease of pitch setting of the airscrew blades, a manual contro1 to the intake or discharge of said pump to cause said pump to apply a torque through the gear train to the airscrew blades turning them totheir extreme high pitch or feathered position, anda governor screw blades.

13. In a variable pitch airscrew having' two or more blades rotatably mounted on a hub casing and connected together to effect equality of vpitch setting, a central anchoring barrel taking the centrifugal pull .0f all the-blades, a bearing taking the centrifugal pull of each blade carried by the anchoring barrel, a counterweight nearly balancing the aerodynamic and other forces acting oneach blade. a gear train capable of transmitting rotation from either end and connected vat: one end with the airscrew blades, said gear train comprising two stages, the first stage, car-` ried by the airscrew, containing a planetary gear system located concentrically in relation to the airscrew' axis and giving the second stage a mechanical advantage over theblades, a drive ring rotatable about the airscrew axis connecting the two stages of the gear train, a statically mounted l air pump, which may be operated as a motor, connected with the other end of said gear train for pitch changing movement of the blades, a compressor adapted to deliver 'air to the intake of said air pump,`means to control the intake or discharge of said pump to vary the magnitude or reverse the direction of the torque applied by said pump to the gear train to effect increase or decrease of pitch'setting of the airscrew blades,

a manual control to the intake or discharge of said pump to cause said pump to apply a torque through the gear train to the airscrew blades turning them to their extreme high pitch or feathered position, and a governor controlling said means in agreement with variations in rotational speed of the airscrew'from a selectable datum.

- 14. In a variable. pitch airscrew havingtwo or anchoring barrel, a gear train capable of transcontrolling said means in agreement' Vwith varia-v tions in rotational speed of the airscrew from a selectable datum. V

mitting rotation from either end and connected at one end with the airscrew blades, a statically mounted torque producing mechanism connected with the other end of said gear train for pitch changing movement of the blades, said mechanism comprising a plurality of fluid pressure means connected together by a system of conl duits, each of the fluid-pressure means beingv adapted to be operated, with outlet to the other oi' said means, as a pump or as a fluid motor and means' to control said mechanism to vary the torque produced both in magnitude and direcon the blades locating said anchoring barrel, a

counterweight approximately balancing the aerodynamic and other forces acting on each blade, a gear train capable of transmitting rotation from either end and connected at one end with the airscrew blades, said gear train comprising two stages, the first stage, carried by the airscrew, containing a planetary gear system located oo ncentrically in relation to the airscrew axis and giving the second stage a mechanical advantage over the blades, a drive ring rotatable about the airscrew axis connecting the vtwo stages of the gearA train, a statically mounted air pump,'which may be operated as a motor, connected with the other end of said gear train for pitch changing movement of the blades, a compressor adapted to deliver air to the intake of said air pump, means to control the intake or discharge of said pump tc vary the magnitude or reverse the direction of the torque applied by said pump to the gear train to effect increase or decrease of pitch setting of the airscrew blades, a manual control to the intake or discharge of said pump to cause said pump to apply a torque through the gear train to the airscrew blades turning them to their extreme high pitch or feathered position, and a governor controlling said means in agreement with variations in rotational speed of the airscrew from a selectable datum.

.ing said anchoring barrel, a counterweight approximately balancing the aerodynamic and other forces acting on each blade, a gear train capable of transmitting rotation from either end and connected at one end with the airscrew blades, 'said gear train comprising two stages, the rststage carried by the airscrew, containing a planetary gear system located coneentrically in relation to the airscrew axis and giving the second stage a` mechanical advantage over the blades, a drive ring rotatable about theairscrew axis connecting the two stages of the gear train, a statically mounted air pump, which may be operated as a motor, connected with the other end of said gear train for pitch changing movement of the blades, a compressor adapted to deliver air to the intake of said air pump, means to control the intake or discharge of said pump to vary the magnitude or reverse the direction of the torque applied by said pump to the gear traintoeect increase or decrease of pitch setting of the airscrew blades, a manual control to the intake or discharge of said pump to cause said pump to apply a torque through the gear train to the airscrew blades 4-turning them to their extreme high pitch or feathered position, and a governor controlling said means in agreement with variations in rotational speed of the airscrew from a selectable datum.

GRETIIR ALGARSSON. 

